1. Field of the Invention
This invention relates generally to systems and methods for optimizing the performance and minimizing complications related to implanted sensors, such as pressure sensors, for the purposes of detecting, diagnosing and treating cardiovascular disease in a medical patient.
2. Description of the Related Art
There are approximately 60 million people in the U.S. with risk factors for developing chronic cardiovascular diseases, including high blood pressure, diabetes, coronary artery disease, valvular heart disease, congenital heart disease, cardiomyopathy, and other disorders. Another 10 million patients have already suffered quantifiable structural heart damage but are presently asymptomatic. Still yet, there are about 5 million patients with symptoms relating to underlying heart damage defining a clinical condition known as congestive heart failure (CHF). Although survival rates have improved, the mortality associated with CHF remains worse than many common cancers. The number of CHF patients is expected to grow to 10 million within the coming decade as the population ages and more people with damaged hearts survive.
CHF is a condition in which a patient's heart works less efficiently than it should, and a condition in which the heart fails to supply the body sufficiently with the oxygen-rich blood it requires, either during exercise or at rest. To compensate for this condition and to maintain blood flow (cardiac output), the body retains sodium and water such that there is a build-up of fluid hydrostatic pressure in the pulmonary veins that drain the lungs, which is generally equivalent to the left atrial pressure. As hydrostatic pressure exceeds oncotic pressure and lymph flow, fluid transudates from the pulmonary veins into the pulmonary interstitial spaces, and eventually into the alveolar air spaces. This complication of CHF is called pulmonary edema, which can cause shortness of breath, hypoxemia, acidosis, respiratory arrest, and death. Although CHF is a chronic condition, the disease often requires acute hospital care. Patients are commonly admitted for acute pulmonary congestion accompanied by serious or severe shortness of breath.
One relatively new approach for treating cardiovascular disease is to implant sensors, such as pressure sensors in various chambers of the heart or adjacent vasculature such as the pulmonary arteries or veins, for the purposes of detecting early cardiac decompensation and prevention of pulmonary congestion and edema. Another potential advantage of implanted pressure transducers is that they may be useful in preventing overtreatment with resultant hypoperfusion of vital organs such as the kidneys. Such an approach utilizing a left atrial pressure transducer coupled with a medical therapy optimization system is described by Eigler et al. in U.S. Pat. No. 6,328,699, herein incorporated by reference.
One particular type and method of sensor placement is known as transmural placement where the sensor device enters the desired location by perforation of the tissue wall separating the outside the structure to inside the structure. Generally the sensor device resides on both sides and within a wall separating parts of the body, parts of an organ such as the heart, or separating a body structure form the rest of the body (the wall of a blood vessel). Sensor packages can be transmurally placed in the left atrium of the heart by a minimally invasive percutaneous catheter based procedure known as transseptal catheterization as originally described by Ross (Ross, J., Jr.: Transseptal left heart catheterization: A new method of left atrial puncture. Ann. Surg. 1949:395, 1959) and Cope in 1959 (Cope, C.: Technique for transseptal catheterization of the left atrium: Preliminary report. J. Thorac. Surg. 37:482, 1959), and modified by Brockenbrough and Braunwald in 1960 (Brockenbrough E C, Braunwald E: A new technique for left ventricular angiocardiography and transseptal left heart catheterization. Am J Cardiol 6:1062, 1960) and subsequently by Ross in 1966 (Ross J Jr.: Considerations regarding the technique for transseptal left heart catheterization. Circulation 34:391, 1966), all herein incorporated by reference. More invasive surgical procedures can transmurally place sensor devices in any cardiac chamber or blood vessel of sufficient size including the pulmonary arteries and veins.
Implantable pressure transducers are known in the art. For example, U.S. Pat. Nos. 4,023,562, 4,407,296, 4,407,296, 4,485,813, 4,432,372, 4,774,950, 4,899,751, 4,899,752, 4,986,270, 5,027,816, 4,353,800, 4,846,191, and 6,379,308 describe various types of pressure sensors. However, pressure sensors that are currently described in the art are not suitable for chronic implantation in the body for several reasons. For example, some pressure transducers are not hermetically sealed, or otherwise properly protected, and thus susceptible to degradation by bodily fluids. Other transducers are constructed such that their specific geometries or components cause thrombus formation, a potentially life threatening condition. Several transducers are constructed in a manner that result in significant “drift” of the pressure sensor, either due to tissue overgrowth or some other mechanism, thus resulting in inaccurate pressure measurements, which in many cases cannot be properly or easily recalibrated. Thus, there still remains a need in the art for an implantable sensor, such as a pressure transducer, that is stable, safe, effective, accurate, and, if needed, easily recalibrated.